Exhaust gas from internal combustion engines, such as gasoline direct injection, homogeneous charge-compression ignition (HCCI), lean burn gasoline direct injection, alcohol fueled, and the like, includes particulate matter or soot that can contribute to environmental pollution. As such, an exhaust system of the engine may be fitted with a particulate filter that traps the particulate matter. After the engine has run for some time, the particulate filter needs to be cleared of the particulate matter through a regeneration process.
In one regeneration process, the particulate filter can be fitted with a microwave source that heats microwave absorbent spots located on a filter element within the particulate filter. The microwave absorbent spots heat to temperatures between about 500-900 deg. C. and ignite the particulate matter to burn it away. An undesirable aspect of this microwave heating method is that a microwave generator and antenna are only about 50% efficient in converting electrical energy to radiated microwave energy. As such, existing microwave heating methods require an undesirable amount of electrical energy in order to be effective.
Referring now FIGS. 1-2, simulation results are shown for a regeneration cycle of such a microwave heated particulate filter. The simulation assumes a filter substrate of the particulate filter is 7 ½ inches in diameter, 8 inches long, and has a channel density of 100 channels per square inch. The simulation assumes a radiated microwave power is 1000 watts (1 KW).
Referring now to FIG. 1, a graph 10 is shown having an x-axis 12 scaled in meters and a y-axis 14 scaled in degrees Kelvin (deg K). The x-axis 12 represents distance into inlet channels of the substrate. The y-axis 14 represents temperature of the accumulated particulate matter in the inlet channels.
A first line 16 indicates the temperatures of particulate matter in the inlet channels after the radiated microwave power has been turned on for eleven seconds. Peaks at locations 18 indicate locations of the microwave absorbent spots. A second line 20 indicates the temperatures of particulate matter in the inlet channels after the radiated microwave power has been turned on for sixty-one seconds. The radiated microwave power was turned off after the sixty-one seconds. The second line 20 shows that the temperatures of the particulate matter accumulated in the inlet channels are higher than in the first line 16.
A third line 22 indicates the temperatures of the inlet channels fifty-nine seconds after the radiated microwave energy was turned off. It can be seen from the third line 22 that the temperatures of a substantial portion of the particulate matter are below the oxidation temperature of the particulate matter, which is between about 773 and 873 deg. K. (500 and 600 deg. C.). The third line 22 therefore indicates that the oxidation reaction in the accumulated particulate matter extinguished before substantially all of the particulate matter oxidized.
Referring now to FIG. 2, a graph 30 is shown that correlates with the graph 10 if FIG. 1. The graph 30 includes an x-axis 32 and a y-axis 34 scaled in meters (m). The x-axis 32 represents distance into the inlet channels. The y-axis 34 represents thickness of the accumulated particulate matter in the inlet channels.
A first line 36 indicates thicknesses of particulate matter on walls of the inlet channels after the radiated microwave power has been turned on for the eleven seconds. Valleys at positions 18 indicate the locations of the microwave absorbent spots. A second line 40 indicates thicknesses of particulate matter on the walls of the inlet channels after the radiated microwave power has been turned on for the sixty-one seconds. The radiated microwave energy was turned off after the sixty-one seconds.
A third line 42 indicates thicknesses of particulate matter on the walls of the inlet channels fifty-nine seconds after the radiated microwave energy was turned off. The third line 42 shows that the thicknesses of particulate matter between about 0.01 m and 0.05 m (see inside dashed circle 44) into the inlet channels changed little from the first line 36. Since the particulate matter did not combust in that region it is apparent that that region of the inlet channels did not regenerate.
From FIGS. 1 and 2 it can be seen that the heated particulate filter is unable to completely regenerate without undesirably providing it with additional electrical energy. The additional electrical energy could be used to heat more and/or larger microwave absorbent spots and/or continue the radiated microwave power for longer than the sixty-one seconds. Any of these options could undesirably discharge a charging system and/or battery associated with the engine.